Total mercury in the water column near the shelf edge of the European continental margin

Abstract

The purpose of this paper is to investigate the distribution and the relative importance of processes that affect mercury distribution in the water column at the shelf edge of the Celtic Sea, on the western European continental margin. The water column, down to 4500 m, was sampled during two cruises, one in winter 1994 and the other in June 1995, on eight stations. Total mercury concentrations ranged from 0.29 to 9.37 pM with the extreme values in the first 200 m. The highly variable concentrations in the surface layers are attributed to intense atmospheric-sea water exchange processes. The low concentrations encountered in the shelf water prelude any significant influence of continental waters in this area. In the mixed layer, biological uptake and regenerative processes appear to dominate in controlling the vertical mercury distribution. The intermediate and deep-water mercury distribution is mainly governed by the hydrographic features. In summer, a mercury enrichment was observed in the upwelling zone of the shelf break. Mean mercury concentration in the Lower Deep Water (LDW) was typically 1.96±0.23 pM and in the Labrador Sea Water (LSW) 1.97±0.63 pM. The Mediterranean Intermediate Water (MIW) revealed similar levels, with a mean mercury concentration of 2.04±0.84 pM. Between LDW and LSW, the Iceland-Scotland Overflow Water (SOW) exhibited higher concentrations (2.76±0.35 pM). The upper part of the North East Atlantic Central Water (NEADW) and lower part of the North Atlantic Deep Water (NEACW) were characterized by marked peaks of concentration, which are interpreted in term of atmospheric influence and particle regeneration.

A mass balance inventory of mercury in the Arctic Ocean

“…Given the small volume of inflow (Table 2), the best estimate Pacific contribution to the Arctic is 3.9 t year −1 , which is an order of magnitude smaller than the North Atlantic contribution of 44.2 t year −1 based on a mean seawater Hg concentration of 0.40 ng L −1 . [78] For calculation purposes, we have assumed outflows through the Canadian Archipelago and Fram Strait were equivalent to the inflows through the Bering Strait and the Barents Sea, respectively, plus a small additional outflow (3090 km 3 year −1 , divided between the two outlets) to account for freshwater inflows to the ocean. Best estimate concentrations of 0.50 and 0.48 ng L −1 , respectively (Table 2), give Hg effluxes of 13.6 and 53.9 t year −1 .…”

“…Faroes-UK-Scandinavia Best estimate from Cossa et al [78] Archipelago outflow (including waters of the Archipelago and Davis Strait) Resolute Passage, Ellesmere Is. St. Louis et al [54] MeHg only (30-45% of total Hg)…”

The geochemical behavior and isotopic composition of Hg in a mid-Pleistocene western Mediterranean sapropel

“…A growing body of evidence suggests that Hg is strongly associated with organic matter in the modern ocean. Profiles of seawater Hg exhibit minimum concentrations in the photic zone, with stable or slightly increasing concentrations with depth (Cossa et al, 1997;Ferrara et al, 2003;Cossa et al, 2004;Laurier et al, 2004;Kotnik et al, 2007). Photochemical and biological reduction of Hg(II) with subsequent evasion of Hg(0) likely contribute to the photic zone Hg concentration minima (Cossa et al, 1997;Kotnik et al, 2007).…”

Trace metal incorporation in otoliths of a territorial coral reef fish (Abudefduf saxatilis) as an environmental monitoring tool

“…In relation to Cd and Hg sources, could come from Orinoco river discharge, which has high levels of these metals (Laya, 1992), and they are being transported along the east coast of Venezuela by the prevailing marine currents in the area (Rojas et al, 2002). Furthermore, these are metals which have biogeochemical behavior similar the ones of nutrients; consequently, upwelling waters may be enriched with some metals, constituting the main source of Hg and Cd to the coastal areas (Cossa et al, 2004, Valdés et al, 2006. On the other hand, laboratory experiments and field evidences have demonstrated that accumulate Zn and Cu in otoliths is predominantly via dietary exposure rather than through waterborne exposure (Campana 1999, Milton et al, 2000, Ranaldi and Gagnon, 2008b.…”